1. Field
Example embodiments of the present invention may relate to a semiconductor memory device, and more particularly, to a multi-bit programming device and a method of multi-bit programming.
2. Description of Related Art
A non-volatile memory (NVM) device is a type of memory, which can electrically program and erase, and maintain programmed data even when power is not supplied thereto.
NVM devices are widely used for digital cameras, cellular phones, personal data assistants (PDAs), laptop computers, and the like. Also, an NVM device is capable of storing a large amount of data in a relatively small package.
In general, an NVM device programs and erases data by changing a threshold voltage of a transistor in a memory cell array. This method is known as a Fowler-Nordheim tunneling (F-N tunneling).
A programming method of storing at least two data bits in a single memory cell is widely used to reduce a size of a semiconductor chip. Such a method is embodied by varying a threshold voltage of a transistor included in a memory cell array by several different gradations. A memory cell array storing data using such a programming method is known as a multi-level cell (MLC).
However, one gradation of the threshold voltage of a transistor should be smaller in comparison with existing single-level programming methods. Accordingly, controlling a gradation of a threshold voltage of a transistor is difficult.
Also, for program data requiring high reliability, e.g., operating systems, firmware, and the like, a multi-bit programming method to prevent generation of errors while programming is required. Accordingly, a more efficient multi-bit programming method in an NVM device may be required.